Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our ability to prepare for future events.
Overview

The Pacific Northwest is home to the Cascadia Subduction Zone, a 1,300 km-long tectonic boundary between the Juan de Fuca and Gorda oceanic plates to the west and the North America continental plate to the east (Fig. 1). The denser oceanic plates are converging with North America and subducting beneath the western edge of the continent. The interface between upper and lower plates is defined by a large fault, called a megathrust, as well as numerous smaller faults that cut through the surrounding crust (Fig. 2). Over time, frictional stresses accumulate along these faults, building slowly until they exceed the fault’s strength, resulting in an earthquake. Subduction zone earthquakes are the largest on Earth, reaching magnitudes in excess of magnitude M9, and are known to generate large tsunamis.
As part of a broader collaborative effort within the USGS (Gomberg and others, 2017) and academia (for example, SZ4D) to advance subduction zone science and improve hazard assessment, we are working with our partners to integrate multi-resolution geophysical imaging and geological sampling to characterize offshore margin morphology, including submarine landslides, sediment delivery systems, seafloor seeps, active faults, and upper plate velocity structure in Cascadia. Because uplift and subsidence associated with megathrust earthquakes often crosses the coastline, coordinated onshore-offshore synthesis is vital to this effort.
Globally observed correlations between marine forearc morphology and structure and megathrust earthquake slip, magnitude, and rupture length along subduction margins suggest possible correlations between seismic slip behavior and morphotectonic variability. Systematic morpho-tectonic analyses in Cascadia highlight distinct along-strike variations in morphology and structure that may reflect spatial variations in megathrust earthquake behavior (Watt and Brothers, 2020). Identification and regional mapping of active fault structures will enable further investigation of the links between megathrust behavior and upper plate morpho-tectonics. We plan to investigate the relationships between offshore geologic structure, seafloor morphology, seafloor seeps, and sediment dispersal pathways and depocenters. These efforts will help to identify potential tsunamigenic faults, offshore areas prone to strong shaking, portions of the slope susceptible to landslides, and/or optimal environment(s) for marine paleoseismology studies. Together, this information will provide information fundamental to improving regional hazard assessments and our ability to prepare for future events.
Key scientific questions

- To what extent and how frequently do potentially tsunamigenic upper plate structures rupture with the megathrust?
- How do along strike variations in the morphology and structure of the overriding plate relate to possible segmentation of the megathrust?
- How do the material properties of the wedge vary along the margin, and does this influence the behavior of the underlying megathrust fault?
- How is sediment delivered and redistributed across the continental shelf and slope, and how does that influence the geologic record of past events?
- How does earthquake shaking translate to slope failure, and which areas may be prone to failure in the future?
- What is the role of fluids in subduction zone processes and related hazards?
- How is strain partitioned offshore within the overriding plate?
Main Goals
- Acquire state-of-the-art high-resolution bathymetric, seismic-reflection, ocean bottom seismometer (OBS), and sediment core data across the offshore Cascadia margin
- Apply advanced geophysical and core processing techniques and integrative analyses to identify and characterize submarine active faults, landslides, and sedimentation patterns that may present potential hazards to coastal areas
- Work with scientists on land to link processes and hazards across the shoreline
Targeted Products
- Earthquake recurrence history
- 3D fault/geologic model
- Quaternary sediment distribution and properties
- Bathymetry/backscatter and seep distribution
- Hazard maps: earthquake, landslide, and tsunami
- Event response, such as rapid OBS deployments
Fieldwork Timeline

Fieldwork Completed

Since 2018, the USGS and its partners have completed several research cruises spanning the entire U.S. Cascadia margin (Fig. 3).
- 2018 USGS-NOAA multibeam bathymetry surveys
- 2018 Regional geophysical surveys of southern Cascadia (offshore northern California and southern Oregon)
- 2019 Regional geophysical surveys of northern and central Cascadia (offshore Washington and Oregon)
- 2019 Geophysical surveys and instrumented tripod deployment in and around Astoria Canyon
- 2019 USGS-NOAA Multibeam Bathymetry
- 2019 Seafloor Geodesy cruise
- 2019 Lake Ozette
- 2019 Geophysical surveys and sediment coring in southern Cascadia (northern California)
- Margin-wide Cascadia seismic reflection imaging and ocean bottom sensor deployments [See also, the informational sheet]
- “Unlocking plate motions of the Cascadia subduction zone with seafloor geodesy” — Set two new geodesy sites March 12-17, 2021
Partners/Collaborators
Federal: NOAA, BOEM, NSF, EXPRESS, U.S. National Park Service, and scientists from multiple USGS Mission Areas (Natural Hazards, Ecosystems, Core Science Systems, Energy and Minerals)
State: California Geological Survey, Washington Department of Natural Resources (DNR)
Academic: University of Washington, Humboldt State University, Oregon State University, Scripps Institution of Oceanography, University of Hawaii, Woods Hole Oceanographic Institution
Private: MBARI, Ocean Exploration Trust
Related USGS Projects
John Wesley Powell Center for Analysis and Synthesis Working Groups
- Margin-wide geological and geophysical synthesis to understand the recurrence and hazards of great subduction zone earthquakes in Cascadia
- Tsunami Source Standardization for Hazards Mitigation in the United States
Related news
“Deciphering Cascadia’s history of mega-earthquakes using MBARI’s unique deep-sea vehicles”
- MBARI’s 2019 online annual report
Below are related USGS science projects.
Cascadia Subduction Zone Database
Local Tsunamis in the Pacific Northwest
In the past century, several damaging tsunamis have struck the Pacific Northwest coast (Northern California, Oregon, and Washington). All of these tsunamis were distant tsunamis generated from earthquakes located far across the Pacific basin and are distinguished from tsunamis generated by earthquakes near the coast—termed local tsunamis.
EXPRESS: Expanding Pacific Research and Exploration of Submerged Systems
Tsunami and Earthquake Research
Margin-wide geological and geophysical synthesis to understand the recurrence and hazards of great subduction zone earthquakes in Cascadia
Below are data releases associated with this project.
Cascadia subduction zone database: compilation of published datasets relevant to Cascadia subduction zone earthquake hazards and tectonics (2022)
Composite multibeam bathymetry surface and data sources of the southern Cascadia Margin offshore Oregon and northern California
Multichannel sparker seismic reflection data of USGS field activity 2018-658-FA collected between Cape Blanco and Cape Mendocino from 2018-10-04 to 2018-10-18
Archive of boomer sub bottom data collected off shore Eureka, California during USGS field activity W-1-96-NC from 1996-06-29 to 1996-07-07
Below are publications associated with this project.
Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary
Toward an integrative geological and geophysical view of Cascadia subduction zone earthquakes
Systematic characterization of morphotectonic variability along the Cascadia convergent margin: Implications for shallow megathrust behavior and tsunami hazards
Submarine canyons, slope failures and mass transport processes in southern Cascadia
Cascadia subduction zone database: compilation of published datasets relevant to Cascadia subduction zone earthquake hazards and tectonics
As part of the USGS Powell Center working group on Cascadia earthquake hazards, we compile and host several available geologic, paleoseismic, geophysical, and instrumental datasets along the Cascadia subduction zone. The ArcGIS online map and downloadable map package include both raster images and shapefiles. In this Story Map, we outline the features and datasets compiled.
Below are news stories associated with this project.
Work on this project is collaborative, with federal, state, academic, and private partners listed here, as well as with scientists from multiple USGS Mission Areas: Natural Hazards, Ecosystems, Core Science Systems, and Energy and Minerals.
- Overview
Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our ability to prepare for future events.
Overview
Sources/Usage: Public Domain. Visit Media to see details.Topo-bathymetric map of the Cascadia subduction zone. Cascadia megathrust fault (white line); approximate shelf break along 200-m isobath (yellow line); MTJ, Mendocino triple junction. The Pacific Northwest is home to the Cascadia Subduction Zone, a 1,300 km-long tectonic boundary between the Juan de Fuca and Gorda oceanic plates to the west and the North America continental plate to the east (Fig. 1). The denser oceanic plates are converging with North America and subducting beneath the western edge of the continent. The interface between upper and lower plates is defined by a large fault, called a megathrust, as well as numerous smaller faults that cut through the surrounding crust (Fig. 2). Over time, frictional stresses accumulate along these faults, building slowly until they exceed the fault’s strength, resulting in an earthquake. Subduction zone earthquakes are the largest on Earth, reaching magnitudes in excess of magnitude M9, and are known to generate large tsunamis.
As part of a broader collaborative effort within the USGS (Gomberg and others, 2017) and academia (for example, SZ4D) to advance subduction zone science and improve hazard assessment, we are working with our partners to integrate multi-resolution geophysical imaging and geological sampling to characterize offshore margin morphology, including submarine landslides, sediment delivery systems, seafloor seeps, active faults, and upper plate velocity structure in Cascadia. Because uplift and subsidence associated with megathrust earthquakes often crosses the coastline, coordinated onshore-offshore synthesis is vital to this effort.
Globally observed correlations between marine forearc morphology and structure and megathrust earthquake slip, magnitude, and rupture length along subduction margins suggest possible correlations between seismic slip behavior and morphotectonic variability. Systematic morpho-tectonic analyses in Cascadia highlight distinct along-strike variations in morphology and structure that may reflect spatial variations in megathrust earthquake behavior (Watt and Brothers, 2020). Identification and regional mapping of active fault structures will enable further investigation of the links between megathrust behavior and upper plate morpho-tectonics. We plan to investigate the relationships between offshore geologic structure, seafloor morphology, seafloor seeps, and sediment dispersal pathways and depocenters. These efforts will help to identify potential tsunamigenic faults, offshore areas prone to strong shaking, portions of the slope susceptible to landslides, and/or optimal environment(s) for marine paleoseismology studies. Together, this information will provide information fundamental to improving regional hazard assessments and our ability to prepare for future events.
Key scientific questions
Sources/Usage: Public Domain. Visit Media to see details.Schematic cross-section of the accretionary wedge along the Cascadia subduction zone. Modified from Moore and others, 2007. - To what extent and how frequently do potentially tsunamigenic upper plate structures rupture with the megathrust?
- How do along strike variations in the morphology and structure of the overriding plate relate to possible segmentation of the megathrust?
- How do the material properties of the wedge vary along the margin, and does this influence the behavior of the underlying megathrust fault?
- How is sediment delivered and redistributed across the continental shelf and slope, and how does that influence the geologic record of past events?
- How does earthquake shaking translate to slope failure, and which areas may be prone to failure in the future?
- What is the role of fluids in subduction zone processes and related hazards?
- How is strain partitioned offshore within the overriding plate?
Main Goals
- Acquire state-of-the-art high-resolution bathymetric, seismic-reflection, ocean bottom seismometer (OBS), and sediment core data across the offshore Cascadia margin
- Apply advanced geophysical and core processing techniques and integrative analyses to identify and characterize submarine active faults, landslides, and sedimentation patterns that may present potential hazards to coastal areas
- Work with scientists on land to link processes and hazards across the shoreline
Targeted Products
- Earthquake recurrence history
- 3D fault/geologic model
- Quaternary sediment distribution and properties
- Bathymetry/backscatter and seep distribution
- Hazard maps: earthquake, landslide, and tsunami
- Event response, such as rapid OBS deployments
Fieldwork Timeline
Sources/Usage: Public Domain. Visit Media to see details.Fieldwork Completed
Sources/Usage: Public Domain. Visit Media to see details.Figure 3. Index map of U.S. Cascadia margin showing where data have been collected since 2018 as part of the Subduction Zone Marine Geohazards Project. Details of each survey effort are provided. Since 2018, the USGS and its partners have completed several research cruises spanning the entire U.S. Cascadia margin (Fig. 3).
- 2018 USGS-NOAA multibeam bathymetry surveys
- 2018 Regional geophysical surveys of southern Cascadia (offshore northern California and southern Oregon)
- 2019 Regional geophysical surveys of northern and central Cascadia (offshore Washington and Oregon)
- 2019 Geophysical surveys and instrumented tripod deployment in and around Astoria Canyon
- 2019 USGS-NOAA Multibeam Bathymetry
- 2019 Seafloor Geodesy cruise
- 2019 Lake Ozette
- 2019 Geophysical surveys and sediment coring in southern Cascadia (northern California)
- Margin-wide Cascadia seismic reflection imaging and ocean bottom sensor deployments [See also, the informational sheet]
- “Unlocking plate motions of the Cascadia subduction zone with seafloor geodesy” — Set two new geodesy sites March 12-17, 2021
Partners/Collaborators
Federal: NOAA, BOEM, NSF, EXPRESS, U.S. National Park Service, and scientists from multiple USGS Mission Areas (Natural Hazards, Ecosystems, Core Science Systems, Energy and Minerals)
State: California Geological Survey, Washington Department of Natural Resources (DNR)
Academic: University of Washington, Humboldt State University, Oregon State University, Scripps Institution of Oceanography, University of Hawaii, Woods Hole Oceanographic Institution
Private: MBARI, Ocean Exploration Trust
Related USGS Projects
John Wesley Powell Center for Analysis and Synthesis Working Groups
- Margin-wide geological and geophysical synthesis to understand the recurrence and hazards of great subduction zone earthquakes in Cascadia
- Tsunami Source Standardization for Hazards Mitigation in the United States
Related news
“Deciphering Cascadia’s history of mega-earthquakes using MBARI’s unique deep-sea vehicles”
- MBARI’s 2019 online annual report - Science
Below are related USGS science projects.
Cascadia Subduction Zone Database
-a compilation of published datasets relevant to Cascadia subduction zone earthquake hazards and tectonics The following is new (2022) compilation of datasets relevant to Cascadia subduction zone earthquake hazards and tectonics useful for emergency management officials, geologists, and others interested in understanding the unique geologic dynamics that create hazards to communities in the region...Local Tsunamis in the Pacific Northwest
In the past century, several damaging tsunamis have struck the Pacific Northwest coast (Northern California, Oregon, and Washington). All of these tsunamis were distant tsunamis generated from earthquakes located far across the Pacific basin and are distinguished from tsunamis generated by earthquakes near the coast—termed local tsunamis.
EXPRESS: Expanding Pacific Research and Exploration of Submerged Systems
EXPRESS is a multi-year, multi-institution cooperative research campaign in deep sea areas of California, Oregon, and Washington, including the continental shelf and slope. EXPRESS data and information are intended to guide wise use of living marine resources and habitats, inform ocean energy and mineral resource decisions, and improve offshore hazard assessments.ByCoastal and Marine Hazards and Resources Program, Pacific Coastal and Marine Science Center, 3-D CT Core Imaging Laboratory, Core Preparation and Analysis Laboratory and Sample Repositories, Multi-Sensor Core Logger Laboratory, Organic Geochemistry Laboratory, Deep Sea Exploration, Mapping and CharacterizationTsunami and Earthquake Research
Here you will find general information on the science behind tsunami generation, computer animations of tsunamis, and summaries of past field studies.Margin-wide geological and geophysical synthesis to understand the recurrence and hazards of great subduction zone earthquakes in Cascadia
The Cascadia Subduction Zone, located in the U.S. Pacific Northwest and southwestern British Columbia, has hosted magnitude ≥8.0 megathrust earthquakes in the geologic past, a future earthquake is imminent, and the potential impacts could cripple the region. Subduction zone earthquakes represent some of the most devastating natural hazards on Earth. Despite substantial knowledge gained from deca - Data
Below are data releases associated with this project.
Cascadia subduction zone database: compilation of published datasets relevant to Cascadia subduction zone earthquake hazards and tectonics (2022)
In this database, we compile and host several available onshore and offshore geologic, paleoseismic, geophysical, and instrumental datasets along the Cascadia subduction zone. The ScienceBase data release and downloadable map package is accompanied by an ArcGIS online map and StoryMap.ByNatural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Earthquake Hazards Program, National Cooperative Geologic Mapping Program, Geology, Minerals, Energy, and Geophysics Science Center, Pacific Coastal and Marine Science Center, Deep Sea Exploration, Mapping and Characterization, Subduction Zone ScienceComposite multibeam bathymetry surface and data sources of the southern Cascadia Margin offshore Oregon and northern California
Bathymetry data from various sources, including newly released 2018 and 2019 multibeam data collected by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS), were combined to create a composite 30-m resolution multibeam bathymetry surface of the southern Cascadia Margin offshore of Oregon and northern California. The bathymetry data are available as a 3Multichannel sparker seismic reflection data of USGS field activity 2018-658-FA collected between Cape Blanco and Cape Mendocino from 2018-10-04 to 2018-10-18
This data release contains processed high-resolution multichannel sparker seismic-reflection (MCS) data that were collected aboard Humboldt State University's R/V Coral Sea in October of 2018 on U.S. Geological Survey cruise 2018-658-FA on the shelf and slope between Cape Blanco, Oregon, and Cape Mendocino, California. MCS data were collected to characterize quaternary deformation and sediment dynArchive of boomer sub bottom data collected off shore Eureka, California during USGS field activity W-1-96-NC from 1996-06-29 to 1996-07-07
This data release contains boomer subbottom data collected in June and July of 1996 on the shelf and slope offshore Eureka, California. Subbottom acoustic penetration spans up to several tens of meters, and is variable by location. This data release contains digital SEG-Y data. The data were collected aboard the R/V Wecoma using a Huntec Hydrosonde Deep-Tow system. - Publications
Below are publications associated with this project.
Reproducibility and variability of earthquake subsidence estimates from saltmarshes of a Cascadia estuary
We examine fossil foraminiferal assemblages from 20 sediment cores to assess sudden relative sea-level (RSL) changes across three mud-over-peat contacts at three salt marshes in northern Humboldt Bay, California (~44.8°N, -124.2°W). We use a validated foraminiferal-based Bayesian transfer function to evaluate the variability of subsidence stratigraphy at a range of 30-6000 m across an estuary. WeAuthorsJason Scott Padgett, Simon E. Engelhart, Harvey M. Kelsey, Robert C. Witter, Niamh CahillToward an integrative geological and geophysical view of Cascadia subduction zone earthquakes
The Cascadia subduction zone (CSZ) is an exceptional geologic environment for recording evidence of land level changes, tsunamis, and ground motion that reveals at least 19 great megathrust earthquakes over the past 10 kyr. Such earthquakes are among the most impactful natural hazards on Earth, transcend national boundaries, and can have global impact. Reducing the societal impacts of future eventAuthorsMaureen A. L. Walton, Lydia M. Staisch, Tina Dura, Jessie Kathleen Pearl, Brian L. Sherrod, Joan S. Gomberg, Simon E. Engelhart, Anne Trehu, Janet Watt, Jonathan P. Perkins, Robert C. Witter, Noel Bartlow, Chris Goldfinger, Harvey Kelsey, Ann Morey, Valerie J. Sahakian, Harold Tobin, Kelin Wang, Ray Wells, Erin WirthByNatural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, National Cooperative Geologic Mapping Program, Geosciences and Environmental Change Science Center, Pacific Coastal and Marine Science Center, Core Preparation and Analysis Laboratory and Sample Repositories, Deep Sea Exploration, Mapping and Characterization, Subduction Zone ScienceSystematic characterization of morphotectonic variability along the Cascadia convergent margin: Implications for shallow megathrust behavior and tsunami hazards
Studies of recent destructive megathrust earthquakes and tsunamis along subduction margins in Japan, Sumatra, and Chile have linked forearc morphology and structure to megathrust behavior. This connection is based on the idea that spatial variations in the frictional behavior of the megathrust influence the tectono-morphological evolution of the upper plate. Here we present a comprehensive exaAuthorsJanet Watt, Daniel S. BrothersSubmarine canyons, slope failures and mass transport processes in southern Cascadia
The marine turbidite record along the southern Cascadia Subduction Zone has been used to interpret paleoseismicity and suggest a shorter recurrence interval for large (>M7) earthquakes along this portion of the margin; however, the sources and pathways of these turbidity flows are poorly constrained. We examine the spatial distribution of sediment storage, downslope transport, and slope failures aAuthorsJenna C. Hill, Janet Watt, Daniel S. Brothers, Jared W. Kluesner - Web Tools
Cascadia subduction zone database: compilation of published datasets relevant to Cascadia subduction zone earthquake hazards and tectonics
As part of the USGS Powell Center working group on Cascadia earthquake hazards, we compile and host several available geologic, paleoseismic, geophysical, and instrumental datasets along the Cascadia subduction zone. The ArcGIS online map and downloadable map package include both raster images and shapefiles. In this Story Map, we outline the features and datasets compiled.
- News
Below are news stories associated with this project.
- Partners
Work on this project is collaborative, with federal, state, academic, and private partners listed here, as well as with scientists from multiple USGS Mission Areas: Natural Hazards, Ecosystems, Core Science Systems, and Energy and Minerals.
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